Ion implantation as practiced in semiconductor manufacturing involves deposition of a chemical species into a substrate, such as a microelectronic device wafer, by impingement of energetic ions of such species on the substrate. In order to generate the ionic implantation species, the dopant gas, which may for example comprise a halide or hydride of the dopant species, is subjected to ionization. This ionization is carried out using an ion source to generate an ion beam.
Once generated at the ion source, the ion beam is processed by extraction, magnetic filtering, acceleration/deceleration, analyzer magnet processing, collimation, scanning and magnetic correction to produce the final ion beam that is impinged on the substrate.
Various types of ion sources have been developed, including inductively heated cathode ion sources, Freeman, Bernas, and various others, but regardless of the specific type of ion source employed, the ion source must be capable of continuous operation for extended periods of time, without the occurrence of “glitching” or other impairment that would necessitate shut-down, maintenance or repair of the ion source. Accordingly, ion source lifetime is a critical characteristic of the ion implantation system, as regards the efficient and cost-effective operation of the system.
Ion source failures are attributable to various causes, including accumulation of deposits on cathode surfaces that negatively affect thermionic emission of ions, resulting in lowered arc currents, reduced performance and shortened lifetime of the ion source, as well as deleterious etching reactions from such dopant gases as germanium tetrafluoride as a result of the generation of free fluorine in the arc chamber, as well as stripping or sputtering of cathode material resulting in loss of physical integrity of the cathode and consequent reduction of performance and lifetime of the ion source.
In consequence of the need to avoid ion source failures, and to maintain the operating efficiency and lifetime of the ion source at high levels, the art is continually engaged in efforts to enhance lifetime and performance of ion sources in ion implantation systems.